1. Field of the Invention
The present invention relates generally to vacuum packaging systems. In particular, this invention relates to an improved automatic method and apparatus for the vacuum packaging of products between two sheets of plastic film through the use of transverse channels and side ventilation panels.
2. Description of the Prior Art
Vacuum packaging systems are well known in the art. Early vacuum packaging systems such as U.S. Pat. Nos. 2,778,173; 3,255,567; 3,311,517; and 3,216,172 each allow for vacuum sealing of an object sandwiched between two heated sheets of plastic material. There are drawbacks to the air evacuation methods of each of these patents since an opening in the vacuum seal is left after air is removed which opening must be separately closed by a subsequent operation. As a result, the vacuum closure can never be absolute, and there is a risk of introduction of foreign matter after the vacuum process has been completed.
A U.S. Pat. No. 2,778,173 (1957) issued to Taunton discloses a vacuum packaging method wherein two pieces of packaging film sandwiched an article therebetween. One or both of the films are placed on heated dies which create projections on the films. The object is placed between the two films with the projections facing each other. A vacuum is then drawn through an exhausting hole extending through one film and surrounded by projections, thereby removing the air between the object and the two plastic sheets. The sheets can then be heat sealed to close the exhausting hole.
U.S. Pat. Nos. 3,255,567 (1966) and 3,311,517 (1967) to Keslar et al., disclose a bag comprised of two 2-ply layers of plastic material which sandwiches the object to be sealed. The inner ply of each of the two sides of the bag is embossed with a grid of protuberances which provide grooves through which air can escape. Three sides of the bag are sealed and the object is placed between the two layers. The air is then removed through an evacuation apparatus through the open side of the bag. Once the evacuation is completed the open side is heat sealed.
The Piazze invention, U.S. Pat. No. 3,216,172 (1965) shows a method and apparatus for sealing a vacuum packaging bag. The lower side of the bag has an air evacuating opening. A stiff patch is then placed over the opening.
Refinements to the earlier patents described above are disclosed in U.S. Pat. Nos. 3,828,520 and 3,945,172. Both of these patents were based on the use of ridges on a lower platen (or preformed lower plastic sheet) which created additional channels through which is evacuated. U.S. Pat. No. 3,828,520 issued to Merritt in 1974 discloses a method of producing an airtight sealed package through the use of a lower platen with raised protuberances which allowed for the removal of air through the channels created by the protuberances. In U.S. Pat. No. 3,945,172 (1975) issued to Johnson, this method was improved upon through the use of a preformed bottom plastic sheet. The preformed bottom plastic sheet provided transverse channels through which air was drawn to assure complete exhaustion of air between the top and bottom sheets. Despite the introduction and use of the additional channels in the lower platen or sheet, these inventions only resulted in an air evacuation rate of between 50% and 60% percent.